The Bones of the Skull. 153 



it is separated by the diastema, in which no teeth occur, from a 

 corresponding but imperfectly differentiated process of the pre- 

 maxilla. 



The palatine process (processus palatinus) extends toward 

 the median plane. It forrns with its fellow of the opposite side 

 about two-thirds of the palatine bridge. 



The orbital process (processus orbitalis) is directed obliquely 

 toward the dorsal surface of the skull. In conjunction with the 

 lacrimal bone and the maxillary process of thg frontal, it forms the 

 anterior orbital rim. It is continuous with the fenestrated portion 

 of the body, and its appearance as a process is largely due to its 

 solid character as compared with the perforated surface lying in 

 front of it. 



The zygomatic process (processus zygomaticus) forms the 

 anterior root of the zygomatic arch, and in the adult condition 

 has fused with it the anterior end of the zygomatic bone. Its 

 ventral angle bea^s a prominent masseteric spine for the attach- 

 ment of the ligament of the masseter muscle. 



The sphenoorbital process (processus sphenoorbitalis) lies 

 on the medial wall of the orbit, in a position opposite to the middle 

 portion of the ridge lodging the posterior cheek-teeth. It forms a 

 stout buttreSiS, the tip of which is applied to the ' anteroventral 

 angle of the frontal bone. In this position it is visible from the 

 orbit, lying between the lacrimal bone and the ethmoidal process, 

 of the orbitosphenoid. 



13. THE PREMAXILLA. 



The premaxilla, or incisive bone (os incisivum), forms the 

 anterior portion of the upper jaw. It comprises a central portion, 

 the body — including with the latter the scarcely differentiated 

 alveolar portion containing the large and small incisors — a 

 frontal process, and a palatine process. The body forms a 

 portion of the palatal surface of the skull and of the lateral boun- 

 dary of the incisive foramen. Its dorsal surface forms part of the 

 boundary of the piriform aperture, the remaining portion of this 



